Protection of pipeline joint connections

ABSTRACT

A method and apparatus for protecting exposed pipeline joints on weight coated pipelines used in offshore applications. The method allows quick installation on a lay barge where pipeline sections are being welded together for offshore installation. The method does not require a long cure time before handling. The method protects the corrosion coating on pipeline joint sections not covered with weight coat by forming a pliable sheet of polyethylene into a cylindrical cover material sleeve over the exposed pipeline joint connection. Polyurethane chemicals are reacted to form a high density foam which fills an annular space between the pipe and the cover material sleeve. The cover material sleeve and the foam form a composite system to protect the joint connection whereby the foam provides continuous compressive reinforcements and impact resistance and the sleeve provides puncture resistance and protection from water jetting/post trenching operations plus abrasion resistance.

This is a divisional of Ser. No. 08/694,397, filed Aug. 12, 1996, nowU.S. Pat. No. 5,900,195

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to pipeline joint protection. More specifically,the invention provides a method and an apparatus for protecting exposedpipe joints on weight coated pipelines used in offshore applications.

2. Description of the Related Art

It has been a common practice in the offshore pipeline industry to useweight coated pipe for pipelines which were to be located on oceanfloors or other underwater surfaces. The weight coats traditionally usedhave been made of dense materials, frequently concrete, applied severalinches thick around the circumference of the pipe. The weight coats wereto protect the pipeline and also to provide sufficient weight tomaintain the pipeline submerged in a non-buoyant condition.

The weight coats usually have been applied to the full length of thepipe except for a short distance, usually about one foot from the end ofeach pipe section. The end portion of the pipe remained without theweight coat to facilitate welding sections of the weight coated pipetogether to make up the pipeline.

Sections of pipe have been placed on a barge and welded sequentiallyonto preceding sections forming a pipeline extending from the barge. Thenewly formed pipeline was on rollers and as the barge moved forward, thepipeline would be carried over the rollers, lowered, and laid on the bedof the body of water.

The portions of the pipe without the weight coat had a corrosion coatingapplied to the surface of the pipe to prevent the pipe from corrodingdue to exposure to the elements. Generally, the corrosion coatings usedwere heat shrinking tape or a fusion bonded epoxy. After the sections ofpipe were welded together various techniques were used to protect thecorrosion coating on the exposed portions of pipe around each joint. onetechnique was to wrap sheet metal over the weight coating adjacent theexposed portion of the pipe and band the sheet metal in place with metalbands. Generally, a 26 to 28 gauge zinc coated sheet metal was used. Thespace between the pipe and sheet metal was then filled with a moltenmastic which would solidify as it cooled. However, in most cases, thepipeline had to be in a condition for handling immediately after thesleeves were filled so that the laying of the pipeline could proceedwithout delays. The mastic filling did not set or harden to asufficiently strong material within the required time to allow furtherprocessing of the pipe and the mastic would leech out into the water ifthe pipeline was lowered before the mastic was adequately cured.

An additional problem associated with this technique was that thebanding used to hold the sheet metal in place, as well as the sheetmetal itself, would corrode after the pipejoint was underwater for aperiod of time. Once the banding corroded, the sharp ends of the sheetmetal would come loose from the pipe. This created a particular problemin areas where commercial fishing was taking place. The sharp sheetmetal ends would cut fishing nets which were being dragged over thepipeline by fishing trawlers. The destruction of fishing nets by theloose sheet metal created severe financial problems for fishingindustries. In some cases, corrosion resistance banding, such asstainless steel banding, was used to avoid this problem, but it was moreexpensive and also subject to eventual failure.

Other techniques replaced the mastic filler with other types ofmaterials. In the method disclosed in U.S. Pat. No. 5,328,648, theexposed portion of pipe was covered with a mold which was then filledwith a filler material. The filler materials were granular orparticulate matter such as gravel or iron ore which would not packsolidly or uniformly. Elastomeric polyurethanes or polyureas were theninjected into the mold in an attempt to fill the interstices between thegranular fill materials. After the polymer components had reactedcompletely the mold would be removed from the surface of the infill.

This method could be difficult to use when the joint protection systemwas applied aboard the lay barge because the filler material, oftengravel, had to be loaded and carried onto the barge. Additionally, therewas often a lack of uniformity in the finished infill resulting fromuneven polymer distribution in the filler material which created voids.Such voids could leave the corrosion coating exposed and subject todamage from fishing trawler nets or other objects moving through thewater which might encounter the submerged pipeline.

Another technique, disclosed in U.S. Pat. No. 4,909,669, involvedwrapping the exposed portions of pipe with a thermoplastic sheet. Thesheet overlapped the ends of the weight coat adjacent the exposed jointand was then secured in place by screws, rivets, or straps. To increasethe rigidity and impact resistance this joint protection system requiredthe installation of reinforcing members such as plastic bars or tubes tothe interior of the sheet. The reinforcement bars or tubes either had tobe precut and stored on the barge or else cut to the required fittingform as part of the installation process on the barge. This requiredadditional handling and made the installation process more difficult.

Another method of reinforcing this joint protection system was to fillthe lower portion of the annular space between the pipe and the plasticsheet with a material such as pre-formed foam half shells. When foamhalf shells were used in the lower portion of the annular space toprovide support, the upper portion of the joint and the corrosioncoating was in effect protected only by the plastic sheet enclosing theupper portion which had no foam covering. This could cause a particularproblem if the pipelines were located where they would encounter thedrag lines or trawler boards attached to the nets of fishing trawlers.The corrosion coating on the upper portion of the pipe joint couldbecome damaged by this type of towed object.

An additional problem with this joint protection system occurred whenpipelines were laid in shallow waters, i.e., less than about 200 feetdeep. Pipelines in shallow waters were often buried by using highpressure water jets which were directed at the ocean floor where thepipelines were to be buried. The water jets would wash out a trench intowhich the pipelines would be dropped for burial. The joint protectionsystem could be damaged when the water jets came in contact with thepipeline joint because the plastic sheet over the top of the pipejointwas not reinforced.

SUMMARY OF THE INVENTION

The present invention provides a method and an apparatus formechanically protecting exposed pipeline joint sections. The methodallows quick installation on lay barges where pipeline sections arewelded together and does not require a long cure time before handling.The method for protecting exposed pipeline joint sections begins byforming a pliable sheet of cover material into a cylinder which isfitted over the exposed portions of the joint connection. Thelongitudinal end portions of the pliable sheet of cover material overlapthe adjacent edges of the weight coating. Side edge portions of thesheet of cover material forming the cylinder are then overlapped tightlysuch that an annular pocket is formed about the exposed joint section.The outside side edge is then sealed to the surface of the sheet ofcover material, completely encasing the exposed pipe and the annularpocket or space. Polyurethane chemicals are then injected into the emptyannular space where they react to form a high density foam which fillsthe annular space. Other polymerizing or hard setting fluid compoundssuch as marine mastics, quick setting concretes, polymers, orelastomeric compounds may also be used to fill the empty annular space.

The present invention provides the joint section of an underwaterpipeline with mechanical protection and abrasion resistance that is notsubject to corrosion problems, will not damage fishing nets, and willnot be damaged by water jets used for pipeline burial.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the invention can be obtained when the detaildescription set forth below is reviewed in conjunction with theaccompanying drawings, in which:

FIG. 1 is a depiction of two sections of weight coated pipe which havebeen joined by welding;

FIG. 2 is a pliable sheet of cover material formed in a cylinder whichis used to enclose the exposed joint section;

FIG. 3 is a longitudinal view, showing the pliable sheet of covermaterial wrapped and sealed around the exposed joint section;

FIG. 4 is a longitudinal cross section showing the joint section afterthe joint protection system has been applied.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a pipeline 10 formed by welding together two pipe sections12 & 12A each of which are covered by a weight coat 14 & 14A,respectively. The weight coat 14 & 14A, which is formed from concrete orother suitable materials, completely covers the pipe sections 16 & 16Acircumferentially and longitudinally except for a portion of each pipeend 18 & 18A of the pipe section 16 & 16A. The pipe ends 18 & 18A areleft exposed to facilitate welding of the two pipe sections 12 & 12Atogether as sections of a pipeline. However, these exposed pipe ends 18& 18A leave gaps of pipe not coated with weight coat in the pipeline 10,which are covered only by a corrosion coating 24.

The method of the present invention begins with installing a covermaterial 30 which is used to enclose and provide structural protectionfor the exposed corrosion coating 24 on the pipe end 18 & 18A. As shownin FIG. 2, the preferred method uses a cover material 30 which ispliable, but strong, and can be formed into a cylindrical shape. Thepreferred cover material 30 is formed from high density polyethylene,however, other thermoplastic materials may be used. The pliable covermaterial 30 should be at least about 0.02 inches thick and may beconsiderably thicker if a stronger support and impact resistance isdesired. Water depth, pipe size, pipe weight and other factors maydictate the use of a cover material 30 which is up to about ½ inch inthickness. The cover material 30 may be a flat sheet or may be preformedinto a cylindrical shape.

The pliable sheet of cover material 30 is wrapped into a cylindricalshape around the exposed pipe ends 18 & 18A such that the insidediameter of the cylinder of cover material 30 is about the same as theoutside diameter of the weight coat 14 & 14A on the pipeline 10. Thecover material 30 should be long enough to overlap the adjacent edges 22& 22A of both sides of the weight coating 14 & 14A by several inches toallow the weight coating 14 & 14A to act as a structural support for thecover material 30. Once the cover material 30 is fitted over theadjacent edges 22 & 22A of the weight coat 14 & 14A, the side edges 34and 36 of cover material 30 are tightly pushed together such that theside edges 34 & 36 overlap. The cover material 30 can be tightened downand held in place with cinch belts. The outside edge 34 is then sealedto the surface of the cover material 30 and a sealed sleeve 40 isformed.

The cover material 30 can be sealed by plastic welding the outside edge34 onto the surface of the cover material 30, forming a longitudinallyextending plastic weld the entire length of the cover material 30 asshown in FIG. 3. Other means of sealing such as heat fusion, riveting,gluing, taping, or banding can also be used to seal the cover material30.

The sealed cover material sleeve 40 forms a protective barrier aroundthe exposed portion of pipe 18 & 18A which remains as a permanent partof the pipeline 10. An annular space 44 is formed around the pipe 18 &18A by installing the cover material sleeve 40. This annular space 44 isfilled by first cutting a hole 38 in the sealed cover material sleeve 40and thereafter injecting fluid joint filler system components throughthe hole 38 and into the annular space 44.

The hole 38 may be drilled or cut or otherwise made in the sealed covermaterial sleeve 40 to thereafter allow unreacted joint filler systemcomponents to be injected into the annular space 44. The hole 38 may beprecut into the cover material 30 prior to installation on the weightcoated pipeline 10 or may be cut after the sealed cover material sleeve40 is in place. The diameter of the hole 38 to be drilled is dependentupon the particular type of mixing head used to inject the joint fillersystem components. Industry standard or conventional injection heads areacceptable.

In the preferred method, the annular space 44 is filled with a highdensity foam by injecting components for a rapid setting polyurethanesystem through the hole 38 with a mixing head. The polyurethane foam 52serves as a shock absorber and protects the corrosion coating on thepipe 18 & 18A. Also, because the foam 52 is open celled, it can absorbwater and increase the ballast effect for the pipeline 10.Alternatively, other polymerizing or hard setting compounds such asmarine mastics, quick setting concretes, polymers, or elastomericcompounds may be used to fill the empty annular space. Preferably, anyalternative filler material is quick hardening, such that the process oflaying the pipeline is not inhibited.

The preferred polyurethane system used to form the protective highdensity foam 52 in this process is a combination of a isocyanate and apolyol system which when reacted rapidly cures and forms high densityopen celled polyurethane foam which resists degradation in sea water.The preferred isocyanate is a polymeric form of diphenylmethanediisocyanate as manufactured by Bayer Corp. The preferred polyol systemis a mixture of multifunctional polyether and/or polyester polyols,catalysts for controlling the reaction rate, surfactants for enhancingcell formation, and water for a blowing agent. Acceptable blended polyolsystem are manufactured by Dow Chemical Co., Bayer Corp., and others.

The preferred polyurethane system produces a foam with a density ofabout 8 to 10 pounds per cubic foot and has about eighty percent orgreater open cells. The compressive strength of the preferredpolyurethane foam is approximately 150 psi or greater at 10 percentdeflection and 1500 psi or greater at 90 percent deflection. Reaction ofthe preferred polyurethane system components can be characterized by a15 to 20 second cream time, the time between discharge from the mixinghead and the beginning of the foam rise, a 40 to 50 second rise time,the time between discharge from the mixing head and the complete foamrise, and a 180 to 240 second cure time, the time required to developthe polymer strength and dimensional stability.

The cover material sleeve 40 acts as a mold and holds the foam 52 inplace until it is completely cured. As shown in FIG. 4, thispolyurethane foam 52 completely fills the annular space 44 withoutleaving significant void areas. No additional filler materials areneeded to be used in conjunction with the polyurethane foam 52. Thepolyurethane foam 52 should completely fill the annular space 44 andprotrude to some extent upward through the hole 38 on the sealed covermaterial sleeve 40.

FIG. 4 shows the completed protective covering of the joint protectionsystem according to the present invention. The sealed cover materialsleeve 40 together with the polyurethane foam 52 provide a protectivesystem which protects the exposed pipe 18 & 18A and the corrosioncoating 24 during handling and laying of the pipeline 10 and continuesto provide protection from damage due to drag lines or trawler boardsattached to fishing trawler nets. Further, the sealed cover materialsleeve 40 is not subject to the corrosion problems of prior art systemsand therefore does not create a underwater hazard or a danger to fishingnets. Additionally, the protective system provided by the presentinvention acts to deflect the high pressure water jets used to burypipelines in shallow waters which have resulted in damage to thecorrosion coating on pipe joints protected by prior art systems.

From the foregoing, it can be seen that the present invention provides amethod and apparatus for protecting the corrosion coating 24 on exposedpipeline joints such as 12 & 12A on weight coated pipelines 10 used inoffshore applications. The method allows quick installation on a laybarge where pipeline sections are being welded together for offshoreinstallation. The corrosion coating 24 on the pipeline joint connections18 & 18A which have no weight coating is protected by forming a pliablesheet of polyethylene into a cylindrical cover material sleeve 40 overthe pipeline joint connection. Polyurethane chemicals are used to reactand form a high density foam 52 which fills the annular space 44 betweenthe pipe 18 & 18A and the cover material sleeve 40. The cover materialsleeve 40 and the foam 52 work together to protect the joint connection.

It should be understood that there can be improvements and modificationsmade of the embodiments of the invention described in detail abovewithout departing from the spirit or scope of the invention as set forthin the accompanying claims.

What is claimed is:
 1. A cover for attachment at positions protectingexposed pipeline joint sections on weight coated offshore underwaterpipelines comprising: a pliable cover material for attachment atpositions overlapping adjacent end portions of the weight coat,completely enclosing the exposed pipe joint section, and sealed in placeforming an annular space around the pipe; said cover material comprisinga sheet of material wrapped in a cylindrical shape and havingoverlapping side edges sealed together to form said annular space; saidannular space between the exposed pipeline and the cover material filledwith a joint filling material of a high density open celled polyurethanefoam, formed by reacting polyurethane chemicals inside the covermaterial; and said cover material including an opening formed in thesheet for injecting the joint filling material into the annular spaceand allow entry of moisture into the polyurethane foam.
 2. The cover ofclaim 1 wherein the pliable cover material is formed from polyethylene.3. The cover of claim 1, wherein the open celled polyurethane foam ofthe joint filling material absorbs moisture when underwater to increaseballast of the pipeline.
 4. The cover of claim 1, wherein the covermaterial is between about 0.02 inches to about 0.5 inches in thickness.5. The cover of claim 1, wherein the opening in the cover material issized to receive a mixing head for injecting the polyurethane chemicalsand prevent escape thereof from the cover material.
 6. A cover attachedon weight coated offshore underwater pipelines at positions forprotecting exposed pipeline joint sections of the pipeline, comprising:a pliable cover material for attachment at positions overlappingadjacent end portions of the weight coat, completely enclosing theexposed pipe joint section, and sealed in place forming an annular spacearound the pipe; said cover material comprising a sheet of materialwrapped in a cylindrical shape and having overlapping side edges sealedtogether to form said annular space; said annular space between theexposed pipeline and the cover material filled with a joint fillingmaterial of a high density open celled polyurethane foam, formed byreacting polyurethane chemicals inside the cover material; and saidcover material including an opening formed in the sheet for injectingthe joint filling material into the annular space and allow entry ofmoisture into the polyurethane foam.
 7. The cover of claim 6, whereinthe pliable cover material is formed from polyethylene.
 8. The cover ofclaim 6, wherein the open celled polyurethane foam of the joint fillingmaterial absorbs moisture when underwater to increase ballast of thepipeline.
 9. The cover of claim 6, wherein the cover material is betweenabout 0.02 inches to about 0.5 inches in thickness.
 10. The cover ofclaim 6, wherein the opening in the cover material is sized to receive amixing head for injecting the polyurethane chemicals and prevent escapethereof from the cover material.